1. Field of the Invention
The present invention relates to an automotive dual air-conditioning system and, more particularly, to a dual air-conditioning system for an automobile in which two sets of air conditioners are arranged, and the operating condition of one air conditioner and the other air conditioner can be controlled simultaneously by controlling the one air conditioner.
2. Description of Related Art
In some types of automobiles, a conventional automotive air-conditioning system adopted is a so-called dual air-conditioning system which includes No. 1 air conditioner located at the front part and No. 2 air conditioner at the rear part. In the automotive dual air-conditioning system, No. 1 air conditioner and No. 2 air conditioner are connected by a bus line. It is possible not only to set the operating condition of No. 1 air conditioner by controlling the operating condition of No. 1 air conditioner by means of various control buttons arranged on a No. 1 air conditioner control panel but to set the operating condition of No. 2 air conditioner according to air-conditioner control information supplied to No. 2 air conditioner through the bus line from No. 1 air conditioner.
No. 1 air conditioner used in the automotive dual air-conditioning system has a control panel, on which temperature setting button, air volume (fan) control button, air outlet select button, outside/inside air changeover button, auto/manual changeover button, and No. 2 air conditioner manual setting button. No. 2 air conditioner has, on its control panel, a temperature setting control unit, air volume (fan) control unit, and air outlet section button. In this case, No. 2 air conditioner manual setting button located on the control panel for No. 1 air conditioner is usually set in OFF position. In this OFF state, the operating condition of No. 2 air conditioner is set so as to be in the same condition as No. 1 air conditioner as previously stated. On the other hand, when No. 2 air conditioner manual setting button is in ON position, the operating condition of No. 2 air conditioner is set to an operating condition according to control on No. 2 air conditioner side, that is, regardless of the control of No. 1 air conditioner.
In such a known automotive dual air-conditioning system, the condition of operation control of No. 1 and No. 2 air conditioners can be controlled simultaneously by controlling the air-conditioner operation control unit of No. 1 air conditioner side. Therefore, there will occur no different setting between the condition of operation control of No. 1 air conditioner and the condition of operation control of No. 2 air conditioner, thereby enabling to prevent a mismatch between the controlled condition of the air conditioner at the front and that of the air conditioner at the rear, giving no discomfort to the driver of the automobile. In addition, since No. 1 and No. 2 air conditioners are controlled to the same condition, it is possible to dispense with time and labor for separately controlling the operating condition of No. 1 and No. 2 air conditioners.
According to the aforementioned known automotive dual air-conditioning system, No. 2 air conditioner can be set to the same condition of operation as No. 1 air conditioner as described above if No. 1 and No. 2 air conditioners are being properly controlled and the bus line for transferring information about air-conditioner control is normally functioning. However, in the event of a communication error of the bus line between No. 1 and No. 2 air conditioners because of trouble arising with the bus line for some reason, the information about the air-conditioner control cannot be properly transferred from No. 1 air conditioner to No. 2 air conditioner via the bus line. Thereafter, therefore, it becomes impossible to properly set the condition of operation of No. 2 air conditioner.
The known automotive air-conditioning system described above is usually so designed that, in case proper transfer of information about air-conditioner operation control to NO. 2 air conditioner has failed, No. 2 air conditioner will be set to a condition of air-conditioner operation in accordance with a normal air-conditioner control information received last. In No. 2 air conditioner, therefore, if the normal air-conditioner control information received last is the air-conditioner control information fed from No. 1 air conditioner and is not affected by control from the control panel of No. 2 air conditioner, No. 2 air conditioner cannot be controlled by any switch or button on the control panel of No. 2 air conditioner. This uncontrollable state will continue until removal of the bus line trouble and recovery from the communication error in information transfer through the bus line. Then, in case the operating condition of No. 2 air conditioner has become uncontrollable, the setting of the operating condition of No. 1 air conditioner will be not enough to control the inside temperature of the automobile, giving much discomfort to a passenger and the driver as well.